[Minor] Remove unused-but-set variables

[Minor] Remove unused-but-set variables

../src/libserver/url.c: In function ‘rspamd_url_host_set_add’:
../src/libserver/url.c:3808:11: warning: variable ‘k’ set but not used [-Wunused-but-set-variable]
 3808 |  khiter_t k;
      |           ^

../src/lua/lua_task.c: In function ‘lua_task_has_urls’:
../src/lua/lua_task.c:2406:11: warning: variable ‘need_emails’ set but not used [-Wunused-but-set-variable]
 2406 |  gboolean need_emails = FALSE, ret = FALSE;
      |           ^~~~~~~~~~~